1. Field of the Invention
This invention relates to a hot isostatic pressing apparatus (hereinafter abbreviated as "HIP apparatus" for the sake of brevity) adapted to heat a metal or ceramic powder compact or a presintered body thereof to a high temperature in an atmosphere of a high-temperature gas so as to carry out sintering, compression forming, densification or the like.
2. Description of the Prior Art
An HIP apparatus is generally constructed of an HIP treatment vessel and a press frame adapted to hold the vessel under pressure. The treatment vessel houses a heater and a heat-insulating layer. A metal or ceramic powder compact or a presintered body thereof (hereinafter called "object" for simplicity) is placed on the bottom lid of the vessel and a high-pressure inert gas is then charged into the vessel, thereby treating the object at elevated temperature and pressure.
In an HIP apparatus of the above sort, the materials making up its heating facilities such as a heater per se are susceptible to oxidation or sublimation if the bottom lid is lowered to remove a treated object immediately or shortly after completion of its HIP treatment. It is thus indispensable to depressurize the treatment vessel together with a treated object still enclosed therein, to cool down the treatment vessel and treated object over a time period as long as well over ten hours, and then to replace the treated object with a fresh object to be treated. This renders the actual working hours of the expensive HIP vessel, namely, the pressure furnace extremely short. Accordingly, such a conventional HIP apparatus is unavoidably accompanied by an economical disadvantage.
In order to overcome such a disadvantage, the present assignee has already developed an HIP method in which an auxiliary station has been incorporated to effect the preheating or forced cooling at such location and, at the same time, certain improvements have been made to the heat-insulating layer, heater and the like so that, after each HIP treatment, the treated object is immediately removed together with the bottom lid without the necessity of awaiting a reduction in the interior temperature, the treated object and bottom lid are then transferred to a cooling station while isolating the heater and treated object from the surrounding atmosphere and the treatment vessel is on the other hand loaded with a fresh object to be treated. The above HIP method has succeeded in rationalizing the production process.
FIG. 1 illustrates one example of an HIP apparatus equipped with such an auxiliary station. On a table 13', there is mounted an HIP treatment vessel 1 equipped with a top lid 2 and a bottom lid which consists of an upper bottom lid 3 and a lower bottom lid 4. An auxiliary station 15 equipped with a cooling cylinder 11 is arranged on a central horizontal extension of the vessel 1. A carrier 6, which has a center of travel on the central horizontal extension, is provided in such a way that it can travel between the vessel 1 and station 15 along rails 14,14. After completion of each HIP treatment, a press frame 5 is removed from the vessel 1 by means of a press frame moving device 12' and, at a position directly underneath the vessel 1, a mechanism housed within a lifting frame 8 which mechanism includes a lift is driven by a lift motor 10 so that the object, held on the bottom lid, is lowered and removed from the vessel 1. Thereafter, the carrier 6 travels to the auxiliary station 15 by means of a carrier-travelling motor 9 and a car 7.
However, the above HIP apparatus is accompanied by such drawbacks as the requirement of a deep pit as the carrier directly underneath the HIP treatment vessel and the operation and maintenance of its equipment are thus rendered troublesome, thereby encountering inconveniences without exception; and the carrying distance of each object is inevitably long due to the arrangement of the carrier in the pit because the carrier is caused to travel with its center of travelling coinciding with the central horizontal extension of the vessel and auxiliary station. When arranging a plurality of auxiliary stations or treatment vessels side by side on the same central horizontal line, it is necessary to provide a carrier between each two stations or vessels or between each vessel and its corresponding station. An HIP apparatus requires a considerable amount of time for cooling each treated object under pressure. Even if one or more auxiliary stations are incorporated, the HIP apparatus may be used only 2-3 times a day. This means that the carrier is substantially unused, leading to an unavoidable economical demerit.